The present invention relates generally to the field of devices for propelling particulate matter with intent to etch the surface of a target material. More specifically, the present invention relates to a micro abrasive blasting device powered by a pressurized-gas source for use with dental procedures.
Abrasive blasting devices operate on the physical property that gas at a higher pressure flows towards and into gas at lower pressure. When particulate matter is mixed with gas at higher pressure, the gas carries the particulate matter as the gas accelerates and flows to the lower pressure. As the gas and particulate matter blast the target material at high speed, the impact of the particles removes layers of the target material.
This process of material removal is commonly known as etching and also as sandblasting. As the rate of the target material removal increases, the etching process can be utilized for drilling and cutting. More specifically, the aggressiveness of the particulate impact-speed and frequency determine the rate of material removal, and thus whether an abrasive blasting device is useful for polishing, etching, or drilling. Particulate impact-speed and frequency are adjusted by variation of the gas flow rate and gas-to-particulate mixture ratio.
In dentistry this technology is known as micro-abrasion and is used to achieve a variety of goalsxe2x80x94such as to remove foreign material or to dull a shiny surface, roughen or etch the surface to enhance bonding quality, and to remove decay by drilling and cutting tooth structure. Such delicate procedures performed intra-oral require instantaneous response and precise control over the flow of the particle stream to assure that no damage due to over-etching or material scatter occur.
As disclosed in pending U.S. patent application Ser. No. 09/702,270, filled Oct. 30, 2000, great advantages are found over existing abrasion devices by preventing the particulate matter from entering the discharge conduit prior to device use. In addition, the pending application discloses that the regulation of the discharge conduit inlet opening provides a superior method for flow control. Specifically, that the position of the closure cap determines the distance to the discharge conduit inlet, where the gap between the closure cap and the discharge conduit inlet determines the gas-abrasive mixing and flow rate. Adjusting the gap between the closure cap and the discharge conduit inlet regulates these gas-abrasive flow characteristics.
In practice, however, the inventor has determined that the adjustment of the gap between the closure cap and the discharge conduit inlet via displacement of the closure cap was good for flow rate regulation but not for dynamic flow rate control during operation. It was found that the user must use both hands to adjust the closure cap position. That is a result of the cap residing at the pressurized-gas source delivery side of the devicexe2x80x94opposite the discharge nozzle; hence to adjust the closure cap positioning requires the use of a second hand while the first aims the nozzle at the target material.
Improvements on the original patent application are disclosed herein, that facilitate dynamic flow-control during operation using only a single-hand. Existing etching devices use various forms of flow control that reside on the pressurized-gas supply lines upstream of the mixing chamber. The flow control method disclosed herein resides downstream of the mixing chamber. Additionally, the improvements disclosed herein eliminate the need for the discharge conduit cap disclosed in the original patent application, further simplifying the device.
One device that also requires two hands to operate is the Paasche device, U.S. Pat. No. 2,441,441. The Paasche device is still widely used by dentists and provides two flow control mechanisms. The device utilizes a screw mounted into the reservoir closure cap to regulate the amount of abrasive contained in the air stream (Page 3 Col. 1 Lines 46-51). The screw is manually adjusted to regulate the gas-abrasive mixture by providing means for varying the gap between the screw tip and gas-abrasive exit tube. For activating the pressurized-gas flow, a separate on-off valve is provided upstream of the mixing chamber (Page 3 Col. 1 Lines 14-23). To dynamically adjust the airflow of the Passche device, two hands are required. One hand is used to support the device and activate the on-off valve, while the second hand is used to adjust the position of the regulating screw.
The Fernwood et al. device, U.S. Pat. No. 4,941,298 provides a pinch lever mechanism for controlling the compressed air flow (Page 1 col. 2 lines 58-64). The pinch lever causes the compressed air inlet supply tube to collapse shut, thus inhibiting the airflow. This Fernwood et al. pinch lever control mechanism is functionally equivalent to the main control valve of the Jones et al. device U.S. Pat. No. 2,577,465. In Jones et al, the valve is also utilized to control the airflow upstream of the mixing chamber (Page 1, Col. 2, Line 7).
Some abrasion devices have no flow regulation mechanisms and are dependent solely on external flow-control mechanisms. These external flow-control mechanisms are very common in dentistry. Several of these controls exist at every dental chair and dental labs, since most dental instruments connect to a standard dental connector. These common dental flow-control means include on-off valves, flow-rate valves and pressure regulators. Many dental devices are controlled via a foot-operated flow-control valve, which sets the pressurized-gas flow rate delivered at the standard dental-chair connector.
The following apparatusesxe2x80x94by Stark et al., U.S. Pat. No. 4,475,370, Hertz, U.S. Pat. No. 5,839,946, Hertz PCT application 96/11696 filed on Jul. 15, 1996, and Schur et al. U.S. Pat. No. 6,004,191,xe2x80x94rely solely on external flow-control mechanisms upstream of the mixing chamber. These apparatuses provide for simple devices with no moving parts and a single mixing chamber. The mixing chamber has only one port for pressurized gas delivery and only one discharge port for gas-particulate mixture release.
The invention disclosed herein solves the following multiple significant shortcomings with devices that have no flow-control mechanisms and are solely dependent on flow-control mechanisms upstream of the mixing chamber:
1. When the external flow-control valve is initially activated, pressure waves propagate through the device as the mixing chamber builds up pressure. The largest pressure wave is caused at the instant the upstream flow is initiated. This is when the pressure gradient between the mixing chamber pressure and the pressurized-gas source is the greatest. This initial pressure wave causes a large amount of particulate matter to be agitated at once, thus causing an initial burst of abrasive to be released in a dense clump. This abrasive clump release causes an initial puff of abrasive that is inconsistent with the normal pace of particulate delivery during the device operation. This initial blast of abrasive may cause significant damage to the target surface by over etching.
2. Every time the external flow-control valve is activated, there is a delay in operational response as the gas-delivery tubing and mixing chamber pressures increase to the up-stream pressure. During this period of pressurization, the mixing action starts and the gas-particulate mixture progressively begins to flow out of the device. As the device reaches operational pressure level, steady gas-particulate mixture flow is established. This response delay in reaching steady flow at start up leads to discharge of abrasive material that does not possess the necessary particle velocity to perform useful etching. This loss of material leads to extra patient discomfort and more rapid depletion of the abrasive material.
3. Every time the upstream flow is terminated, the device continues to operate as the gas-delivery tubing and mixing chamber pressure is depleted. The period of depressurization is significant to the operation of the device since it reduces the responsiveness of the device to the user. This delay may damage the target surface by over etching as the device continues to dispense abrasive material after the user has turned off the pressurized-gas source controls. In operatory conditions, particulate matter may still be dispensed out of the devices as the dentist pulls the device out of the patient""s mouth. This may expose the patient""s eyes to the abrasive.
In fact, the Schur et al patent utilizes a check-valve for preventing gas flow in direction of the pressurized-gas source; hence forcing the device to continue operation as the mixing chamber pressure is reduced to ambient pressure.
In addition, since the operational control of these existing devices is dependent on external flow control mechanisms, performance levels of these devices vary between pressurized-gas sources. For these devices, the aggressiveness and precision of the etching is thus dependent on the external flow-control mechanism, and its abilities to regulate the upstream pressure and flow-rate. The device and method described herein eliminate the performance variation due to external flow-control mechanisms.
Accordingly, several objects and advantages of the present invention are:
(a) to provide a device with means for precise single-hand regulation of the gas-abrasive flow independent of the external flow-control mechanism.
(b) to provide a device with instantaneous flow start-up response via an integral flow-control means that facilitate the continuous pressurization of the mixing chamber.
(c) to provide a device with instantaneous flow shut-off response via integral flow-control means that instantly terminates the flow out of the device without requiring the depressurization of the mixing chamber.
(d) to provide a device with better operational performance by eliminating puffs of abrasive during flow start-up.
(e) to provide a device with means for precisely regulating the gas-abrasive flow so a single device is able to operate in a wide range of applications, from light etching to drilling and cutting.